Near field magnetic communication is a form of wireless physical layer communication that transmits information by coupling non-propagating, quasi-static magnetic fields between devices. A desired magnetic field can be created by a generator coil which is measured using a detector coil. The signal modulation schemes often used in RF communications (amplitude modulation, phase modulation, and frequency modulation) can also be used in near-field magnetic systems.
Near-field magnetic communication systems are designed to contain transmission energy within the localized magnetic field. This magnetic field energy resonates near the communication system, but does not generally radiate into free space. This type of transmission is referred to as “near-field.” The power density of near-field transmissions attenuates or rolls off at a rate proportional to the inverse of the range to the sixth power (1/range6) or −60 dB per decade.
The use of localized magnetic induction distinguishes near field communications from known far-field radio frequency (RF) and microwave systems in that conventional wireless RF systems use an antenna to generate and transmit a propagated RF wave. In these types of systems, the transmission energy is designed to leave the antenna and radiate into free space. This type of transmission is referred to as “far-field.” The power density of far-field transmissions attenuates or rolls off at a rate proportional to the inverse of the range to the second power (1/range2) or −20 dB per decade.
One concern in wireless communication systems is the assignment and control of the RF frequency spectrum. As more and more wireless communication devices try to co-exist, the demand for available frequencies and clear channels becomes greater. Currently, most wireless communication systems rely on a far-field RF physical communication layer. The far-field propagated signals used in these communication systems can travel miles beyond the desired transmission range, causing interference with other wireless systems. To overcome this interference, each system can increase transmission power or be designed to share much of the same frequency spectrum. This spectrum allocation requires the implementation of complex time and frequency allocation algorithms. However, even with all of these work-around allocation schemes, the RF spectrum is still becoming increasingly crowded. The result is a steadily worsening interference and interoperability problem that simply cannot be overcome by transmitting with more power or moving to more complex and power-intensive frequency-management schemes.
Unlike far-field RF waves, the well defined communication region of magnetic-field energy allows for a large number of near-field magnetic communication systems to be in relatively close proximity while operating on the same frequency. Simultaneous access to a defined frequency spectrum is accomplished by localizing the communication region or spatial allocation and not by the allocation of frequencies or time division.
In practice, far-field RF signals used in existing wireless systems can be unpredictable, especially in urban environments, where frequency spectrum contention, EMI, fades, reflection, and blocking due to interfering obstacles such as buildings, vehicles, and industrial equipment can significantly reduce the effectiveness of current far-field RF systems. In addition, far-field RF systems are highly susceptible to EMI due to the nature of the antenna configurations which are designed to be sensitive to energy excitement of electromagnetic plane waves. In instances when the EMI is near the carrier frequency of a far-field RF system, the EMI will prevent the RF system from receiving transmissions, as the antenna will receive both the EMI signals and the intended RF signal equally well.
Near-field magnetic energy is contained in a magnetic field, forming a tight communication area which provides a high signal-to-noise ratio between devices. These magnetic fields are highly predictable and less susceptible to fading and reflection than RF electromagnetic waves used in current communication systems. In addition, the high signal-to-interference-plus-noise ratio (SINR) of near-field systems is less susceptible to EMI than typical RF systems.
The many advantages of near field communication systems make them useful for radio communication between first responders such as police, emergency, and fire fighters, as well as military communication systems. However, near field communication systems, such as systems using near field magnetic induction, are inherently short range. This short range typically restricts the use of near field communication systems to devices used in short range communication, such as personal area networks.
Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.